Mid-infrared electroluminescence from a Ge/Ge0.922Sn0.078/Ge double heterostructure p-i-n diode on a Si substrate

Abstract

We report the observation of mid-infrared room-temperature electroluminescence from a p-i-n Ge/Ge0.922Sn0.078/Ge double heterostructure diode. The device structure is grown using low-temperature molecular beam epitaxy. Emission spectra under various injection current densities in the range of 318 A/cm2–490 A/cm2 show two distinct profiles peaked at 0.545 eV (2.275 μm) and 0.573 eV (2.164 μm), corresponding to indirect and direct bandgaps of the Ge0.922Sn0.078 active layer, respectively. This work represents a step forward towards the goal of an efficient direct-bandgap GeSn light-emitting device on a Si substrate by incorporating higher Sn content of 7.8% in a diode structure that operates at lower current densities.

Direct gap Ge1-ySny alloys: Fabrication and design of mid-IR photodiodes

“…While stannane SnH 4 is unstable, deuteration increases stability to the point that epitaxy applications become feasible. Long-term storage of SnD 4 for commercial applications has also been demonstrated. 16 The chemistry and applications of group-IV hydrocarbon analogues have been recently reviewed by Rivard.…”

“…A number of groups have utilized this approach to fabricate n-Ge/i-Ge 1-y Sn y /p-Ge heterostructure light emitting diodes (LEDs) in which the GeSn active layers are ensconced by p-and n-type Ge electrodes. 4,5,[22][23][24][25] A drawback of such designs, however, is the formation of two defected Ge 1-y Sn y /Ge interfaces that act as carrier recombination sites, adversely affecting the emission efficiency of the devices. Our previous work in this area was focused on the fabrication of enhanced performance LEDs by adopting improved n-Ge/i-Ge 1-y Sn y /p-Ge 1-z Sn z designs containing a single defected interface.…”

“…17 The alternative SnCl 4 precursor is used in combination with Ge 2 H 6 as the Ge source. 13,14 In a typical growth experiment, the gas ratio is held constant, and the film compositions are varied by changing the growth temperature 18 4 to deposit Sn at low temperatures despite the relatively high strength of the Sn-Cl bond (0.33 eV). 6,18 A possible mechanism leading to Sn incorporation under these circumstances would involve the following reactions:…”

“…We obtained $100 nm thick seed layers, which provide a clean and uniform template that allows optimal epitaxy of subsequent intrinsic layers of Ge 1-y Sn y alloys. As indicated above, these were grown using gas mixtures containing appropriate concentrations of Ge 3 H 8 and SnD 4 . The compounds were combined in a 3-L ampule and diluted with research-grade H 2 to a final pressure of 760 Torr.…”

“…2,3 In spite of this thermodynamic constraint, however, devicequality alloys with very high metastable Sn concentrations are now routinely synthesized. [4][5][6] These metastable alloys are not simple academic curiosities but have been incorporated into real device structures, including optically pumped lasers with compositions reaching 13% Sn, 7 and electroluminescent diodes with Sn concentrations above 10%. 8 While the most recent generation of devices exceed the indirect-to-direct transition concentration y c $ 9% Sn, 9 fulfilling one of the basic goals of Ge 1-y Sn y research, there are fundamental and practical reasons for pursuing the development of Ge 1-y Sn y alloys with Sn concentrations well in excess of y c .…”